How would you describe the Universe--
infinite, eternal?
How about smooth versus bumpy?
In other words, why isn't all of the matter in our Universe
clumped together in one big ball,
or conversely, why isn't it perfectly, evenly distributed?
The texture of our Cosmos reveals
clues about how the Universe formed
and what happened moments after the Big Bang.
To understand this curious composition,
and how it changed over the history of the Universe,
it's helpful to think about the matter in the Universe
as a herd of animals.
I'm Jared Kaplan, and this is "How the Big Bang Governs
the Texture of our Universe."
Picture a herd of zebras hanging out on the savanna.
If you're nearby, maybe you're an elephant
who's gone wandering through the herd,
you can see all of the different things the individual zebras
are doing.
Maybe there are a few more zebras on your left
than on your right.
In other words, from close up, the herd of zebras
looks inhomogeneous.
But if you overlook the scene from a cliff far away,
the zebras all look the same.
In other words, the herd looks smooth or homogeneous.
Why do these animals look different close up
but uniform at long distances?
And what does this phenomena reveal about our Universe?
Let's rewind 13.8 billion years to the Big Bang.
This was the earliest epic in our Universe's history
that we think we understand.
It was a time when the Universe was undergoing a massive growth
spurt known as inflation.
And we call it inflation, because the Universe was
expanding exponentially fast--
much, much faster than it's expanding today.
Inflation left the Universe smooth and empty due
to the extremely rapid expansion.
Inflation's impact on the fabric of spacetime
was so extreme that it led to quantum fluctuations in time.
These delays and advances in time made parts of the Universe
a little bit denser than others.
These small fluctuations led to the structures we see today.
But how?
Gravity acted as an amplifier for those inhomogeneities,
causing them to collapse into stars, galaxies, and clusters,
and leaving behind voids in between these celestial bodies.
This is why on a small scale we have pockets of matter,
like a dazzle of zebras--
and yes, that is what a group of zebras is called--
that appear denser than others.
But our Universe appears homogeneous or smooth
on the largest distant scales.
Inflation kicked off an epic of expansion
that left our Universe more than 27 billion light years across.
And matter on one side of our Universe
hasn't had time to gravitationally attract matter
on the other side of the Universe.
It's just like how zebras might form a dazzle.
They might start out in random places alone, spread evenly
across the savanna.
But over time they begin to wander around,
finding more and more friends, and forming
larger and larger groups.
Here, the friendliness of the zebras
is an analog of the gravitational force,
binding zebras together into many bona fide dazzles,
which appears homogeneous at very large distances.
But it's clumpy close up.
Thinking about inhomogeneity allows
us to understand the structures and voids in our Universe.
It allows us to understand primordial inflation, as well
as the amount of dark matter that was around
during various areas of our Universe's history,
allowing us to characterize the formation of our Universe.
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